Who We Are

An independent organization of leading scientists and journalists researching and reporting the facts about our changing climate and its impact on the public.

What We Do

Climate Central surveys and conducts scientific research on climate change and informs the public of key findings. Our scientists publish and our journalists report on climate science, energy, sea level rise. Read More

About Our Expertise

Members of the Climate Central staff and board are among the most respected leaders in climate science. Staff members are authorities in communicating climate and weather links, sea level rise, climate. Read More

Wedges Reaffirmed

In August 2004, Steve Pacala and I published a paper in Science about climate change mitigation. Its core messages are as valid today as seven years ago, but they have not led to action. Here, I suggest that public resistance can be partially explained by shortcomings in the way advocates of forceful action have presented their case. Addressing these shortcomings might put the world back on the course we identified.

Let’s review the messages in our 2004 paper. The paper assumes that the world wishes to act decisively and coherently to deal with climate change. It makes the case that “humanity already possesses the fundamental scientific, technical and industrial know-how to solve the carbon and climate problem for the next half-century.” This core message surprised many people, because our paper arrived at a time when the Bush administration was asserting that, unfortunately, the tools available were not suited for addressing climate change. Indeed, at a conference I attended at that time, Energy Secretary Spencer Abraham insisted that a discovery akin to the discovery of electricity was required.

Our focus on “the next half century” was novel; the favored horizon at the time was a full century — and still is. We argued that "the next fifty years is a sensible horizon from several perspectives. It is the length of a career, the lifetime of a power plant, and an interval whose technology is close enough to envision."

In a widely reproduced figure, we identified a "Stabilization Triangle," bounded by two 50-year paths. Along the upper path, the world ignores climate change for 50 years and the global emissions rate for greenhouse gases doubles. Along the lower path, with extremely hard work, the rate remains constant. We reported that starting along the flat emissions path in 2004 was consistent with “beating doubling,” i.e., capping the atmospheric carbon dioxide (CO2) concentration at below twice its “pre-industrial” concentration (the concentration a few centuries ago).

The paper is probably best known for having introduced the “stabilization wedges,” a quantitative way to measure the level of effort associated with a mitigation strategy: a wedge of vehicle fuel efficiency, a wedge of wind power, and a wedge of avoided deforestation have the same effect on the carbon dioxide in the atmosphere. Filling the stabilization triangle required seven wedges.

The wedge concept fosters parallel discussion of alternatives and encourages the design of a portfolio of responses. Each wedge is an immense activity. In talks about this work, I like to say that we decomposed a heroic challenge into a limited set of monumental tasks.

In short, in addition to a hopeful message that humanity is not helpless, the paper contains the sobering message that the job ahead is daunting.

Today, nine wedges are required to fill the stabilization triangle, instead of seven. A two-segment global carbon-dioxide emissions trajectory that starts now instead of seven years ago — flat for 50 years, then falling nearly to zero over the following 50 years — adds another 50 parts per million to the equilibrium concentration. The delayed trajectory produces nearly half a degree Celsius (three-quarters of a degree Fahrenheit) of extra rise in the average surface temperature of the earth. (Note that there is a three-year lag in the posting of authoritative global data. We used 2001 data in our 2004 paper, and 2008 data are available now. Thus, available data do not yet reflect the recession. Between 2001 and 2008, the emissions rate climbed by more than a quarter.)

Worldwide, policymakers are scuttling away from commitments to regulations and market mechanisms that are tough enough to produce the necessary streams of investments. Given that delay brings the potential for much additional damage, what is standing in the way of action?

The 2004 "wedges" paper assumed that the objective of global mitigation would require a flat emissions rate for 50 years, followed by a falling rate. Making the same heroic assumption today would result in substantial additional emissions.

Familiar answers include the recent recession, the political influence of the fossil fuel industries, and economic development imperatives in countries undergoing industrialization. But, I submit, advocates for prompt action, of whom I am one, also bear responsibility for the poor quality of the discussion and the lack of momentum. Over the past seven years, I wish we had been more forthcoming with three messages: We should have conceded, prominently, that the news about climate change is unwelcome, that today’s climate science is incomplete, and that every “solution” carries risk. I don’t know for sure that such candor would have produced a less polarized public discourse. But I bet it would have. Our audiences would have been reassured that we and they are on the same team – that we are not holding anything back and have the same hopes and fears.

It is not too late to bring these messages forward.

Unwelcome news

Environmental science has brought unwelcome news – that the actions of our species are capable of changing the planet at global scale. Who wouldn’t much rather live on a larger planet, where our actions mattered less? It is counterproductive for advocates of prompt action on climate change to pretend that the new knowledge has only positive consequences, such as the stimulation of green jobs and elegant new technology. Global prosperity now depends on our species’ success at a totally unfamiliar assignment: to “fit” our many billions of people on this small planet, with its finite resources and finite capacity to withstand pollution. The job will be very hard and will require sustained focus.

Credit: iStockphoto.

Confronted with unwelcome news, human beings often shoot the messenger. Consider two earlier occasions. Galileo argued that the earth wasn’t at the center of the universe. For this, he was excommunicated. Darwin argued that human beings were part of the animal kingdom, and he was cruelly mocked. The idea that humans can’t change our planet is as out-of-date and wrong as the earth-centered universe and the separate creation of Man, but all three ideas have such appeal that they will fade away only very slowly.

In particular, just as steadily stronger evidence for the Copernican model and for evolution only gradually won the day, we should anticipate robust resistance to the message that we are fouling our own nest with fossil fuel emissions and deforestation. Armed with insights from psychology and history, communicators of the climate change threat will more deeply understand the hostility to their message. Perhaps, communication will be more effective when shared concerns are acknowledged.

Incomplete climate science

It would be productive for advocates of prompt action also to concede that the message from climate science is not only unwelcome but also incomplete. Feedbacks from clouds, ice, and vegetation are only partially understood – thwarting precise prediction of future climate. The best and worst future climate outcomes consistent with today’s science are very different.

Pacala calls the worst credible climate outcomes “monsters behind the door.” Among the monsters are a five-meter rise in sea level by the end of this century, major alterations of the global hydrological cycle, major changes in forest cover, and major emissions of greenhouse gases from the tundra. The monsters open their door in a world of very strong positive feedbacks, a world that spirals out of control. Today’s science cannot predict how much atmospheric change would let these monsters in, nor how quickly they could enter.

Policymakers assessing the case for immediate forceful action and members of the general public deciding whether to endorse the policymaker’s decisions want to know the full story – both the average outcomes and the extremes (the “tails” of the distribution). In reaching a judgment about whether to act forcefully now, some will give greater weight to best guesses, others to the tails. The more risk-averse will assign greater weight to the tails.

Why, at the intersection of climate science and climate policy, is there more discussion of average outcomes than nasty ones? As I have speculated in a recent paper, one reason is that average outcomes are safer to talk about, because the science is more solid; there is less risk of being accused of alarmism. Also, acknowledging terrible outcomes of low probability requires acknowledging the other tail – a world with rising emissions but little change for quite a while. I often hear that any concession to benign outcomes (or, more accurately, outcomes that remain benign for a relatively long time) will foster complacency. I don’t understand that fear. In my experience, when I tell someone “we could be lucky,” and then I pause, the listener completes the sentence for me: “or we could be unlucky.” The listener does not hear a lullaby.

Arguments for action based on what we don’t know reinforce those based on what we do know. To build a case on what we don’t know, however, takes courage, because it requires revealing how much experts disagree. There are many contending views about sea-level rise, for example. Advocates resist calling attention to the coexistence of contending expert views – far more certain than I am that lay audiences translate such conflicts into justifications for procrastination. I think it should be possible to convey that earth systems science is an evolving human enterprise where discordant views are the norm, and then to explain why certain issues have proved hard to resolve. My working assumption is that candor creates trust.

Editor's Note: This essay continues on page 2, and includes expert commentary from high level figures in the climate policy community such as: Nicholas Stern, Ralph J. Cicerone, Rep. Rush Holt, David Hawkins, Freeman Dyson, Chris Field and others.